The disclosure relates to a current sensor having a self-test function which ensures that the current sensor operates properly, that is to say the measured values measured by the current sensor are reliable. Such a current sensor is particularly suitable for critical applications, for example for monitoring the battery current in a motor vehicle having a battery module and an electrical drive motor. A second aspect of the disclosure is directed to such a motor vehicle which may be in the form of a microhybrid, a mild hybrid or a full hybrid vehicle or else a pure electric vehicle, for example.
Battery systems for use in motor vehicles of the abovementioned types for providing energy for the drive are called “high-voltage batteries” in order to distinguish them from starter batteries for starting an internal combustion engine. Although vehicles having high-voltage batteries are not yet widespread on the market, a certain prior art has already evolved with regard to the safety components which are required in order to ensure safe operation of the high-voltage battery. FIG. 1 shows a high-voltage battery having safety components required according to the present prior art. The high-voltage battery 10 has a multiplicity of battery cells which are connected in series and are intended to generate the desired high output voltage. The individual cells are monitored by so-called cell sense and control units (CSCs) 11 in order to test their state of charge and avoid overcharging or undercharging of the battery cells. The output voltage from the high-voltage battery 10 is monitored by a total voltage detection means 12a on the battery side. A further total voltage detection means 12b is provided on the drive side. A fuse 13 which opens the circuit in the event of impermissibly high currents is inserted into one of the two current paths. A current sensor for detecting the battery current is also inserted into one of the two current paths. Power contactors 15a and 15b are also provided in each of the two current paths in order to be able to switch the high-voltage power supply system of the motor vehicle such that it is not live, for example in an emergency or for a maintenance measure. A charging current path having a charging contactor 16 and a charging resistor 17 for limiting the charging current are also provided, for example, in parallel with the power contactor 15a in FIG. 1.
The current sensor 14, in particular, is very important when monitoring the proper operation of the high-voltage battery system. The measurement variable recorded by the current sensor 14 is used, for example, to detect impermissibly high battery currents and, if necessary, to take countermeasures in order to keep the system in a safe operating state. The instantaneous state of charge of the high-voltage battery is also calculated from the measured current by means of suitable methods. In addition, the high-voltage battery could be overcharged or undercharged, which entails harmful or even dangerous states of the high-voltage battery.
A plurality of methods exist for detecting the battery current, for example:                measurement by means of a voltage drop across a resistor (shunt principle)        measurement by means of transformers on the basis of the induction principle        measurement by means of Rogowski coils on the basis of the induction principle        measurement of the magnetic field generated by the battery current, for example by means of Hall sensors, magnetoresistive sensors (AMR, GMR)        
A plurality of requirements are imposed on the detection of the battery current, for example a sufficiently high accuracy and bandwidth. The important factor in high-voltage battery systems is also sufficient DC isolation between the high-voltage vehicle power supply system, the measuring electronics and the low-voltage vehicle power supply system (if appropriate with the starter battery) in order to protect the vehicle occupants from hazardous shock currents in the event of a defect in the electronics.
At the same time, the costs of a current sensor are intended to be as low as possible in order to be able to offer the overall system at prices in line with the market. Redundancy by using a plurality of current sensors is therefore not very attractive in economical terms, especially since, when using only two current sensors, it would also not be clear, in the event of differing measured values from the two current sensors, which current sensor is operating correctly and which is not.
The aim of the disclosure is to overcome the abovementioned problems of the prior art.